1. Field of the Invention
The present invention relates to the field of manufacture of liquid crystal displays, and in particular to a method for manufacturing a thin-film transistor (TFT) array substrate with three masking operations.
2. the Related Arts
Nowadays, technology and science have been in prosperous development and progress and information devices are constantly innovated to suit the need of the public. The early displays were mostly cathode ray tube (CRT) displays, which is of a bulky size and a great power consumption and also generates radiations that are dangerous to human body for user operating for a long while. Thus, the displays that are currently available in the market are liquid crystal displays in substitution of the CRT displays.
Liquid crystal displays have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus of wide applications. Most of the liquid crystal displays that are currently available in the market are backlighting liquid crystal displays, which comprise a liquid crystal panel and a backlight module. The operation principle of a liquid crystal panel is that liquid crystal molecules are interposed between two parallel glass substrates and a driving voltage is applied to the two glass substrates to control rotation direction of the liquid crystal molecules in order to refract out light emitting from the backlight module for generating images. Since the liquid crystal panel itself does not emit light, light must be provided from the backlight module in order to normally display images. Thus, the backlight module is one of the key components of a liquid crystal display.
The two parallel glass substrates of the liquid crystal panel are respectively a TFT array substrate and a color filter (CF) substrate. The TFT array substrate comprises: a substrate; gate lines, gate terminals, gate insulation layers, semiconductor active layers, data lines, source terminals, drain terminals, and protective layers formed on the data lines, source terminals, and drain terminals and pixel electrodes formed on the protective layers, wherein the gate terminals, the source terminals, the drain terminals, and the semiconductor active layers constitute thin-film transistors. In the state of the art, the TFT is an amorphous silicon thin-film transistor or a low temperature poly-silicon thin-film transistor. An amorphous silicon TFT display array requires only 3-5 photolithographic masking operations, and this leads to low cost and high competition power. A low temperature poly-silicon TFT display array usually needs 8-9 photolithographic masking operations, making the cost relatively high.
Oxide semiconductor IGZO (Indium Gallium Zinc Oxide) has a carrier mobility that is about 20-30 times of that of amorphous silicone and may greatly increase the charging/discharging speed of a TFT with respect to a pixel electrode thereby improving the response speed of the pixel electrode to achieve increased refreshing rate. Further, the increased response speed also increases, to quite a great extent, row scanning rate of pixels, making it possible to achieve ultra-high definition in a thin-film transistor liquid crystal display (TFT-LCD). Further, since the number of TFTs is reduced and light transmittal of the pixel is enhanced, the IGZO LCD shows high level of performance and increased efficiency. The oxide semiconductor IGZO can be manufactured with an existing amorphous silicon manufacturing line, with just minor modification. This makes it more competitive than low temperature poly-silicon in respect of cost.
However, the manufacture of a TFT with oxide semiconductor IGZO adopts a manufacturing process that requires 6 masking operations so that manufacturing efficiency is low and the manufacturing cost is high.